New to this photography lark, will someone explain why a lens off a SLR will have a different focal length on a DSLR? Something to do with the light sensor?

i think its because the sensor on a dlr is a third larger than 35mm negatives so giving a longer focal lenght

because different sensors have different crops, the cheaper they are the more cropped usually, hence a £2k body camera like a 5dmk2 is full frame but a £700 body camera is a cropped frame making a 50mm lense more like 85mm and so on.

can be good depending on what you want to do ie a f1.8 50mm lense is cheap but a 85mm is expensive… so thats handy but full frame is obviously the most effective of body and lens harmony 🙂

Pedantic point but not un-important. The focal length of the lens is fixed, what changes is the field of view. You only see the centre of a 35mm format lens' image circle on a "regular" DX/aps-c format sensor.

Distortion/flattening of perspective is unchanged, you just see less or more in the frame.

DX format sensors are typically 2/3's the size of a standard 35mm negative, therefore giving approx 1.5 times magnification to any standard 35mm SLR lens, so a standard 50mm gives the equivalent of 75mm and so on…

FX format sensors are the same size as a 35mm negative and therefore a 50mm standard lens remains a 50mm standard lens.

Nothing to do with price at all, although FX cameras are at the higher end, but DX is still high end as well, wildlife/sports photogs can benefit from the DX format, Landscape photogs can benefit from the FX format, horses for courses

Well it is partly to do with price, a big sensor (i.e. full frame) is much much more expensive to manufacture which is why cheap cameras have APS-C size sensors (DX format in Nikon speak).

i think its because the sensor on a dlr is a third larger than 35mm negatives so giving a longer focal lenght

an example of spreading misinformation on the internet.

What Brand are you talking about?
eg, if it's Canon (and not a full frame model – which means there is no crop/difference in effective focal length) then the crop factor is 1.6 times the focal length.

Basically it gives the effect of being zoomed in 1.6 times further, although in reality it just crops what fits onto the sensor. Only important if a) your used to the focal lengths on an Film SLR or b) you are in the club that thinks full frame has a massive impact on images – which it doesn't. (it's like having to have XTR instead of SLX/XT for a weekend warrior!)

That's why I went for 7d but with L lenses. No point of having 5d with crap ones. Even then, for most bestest photos you need to use tri-pod, and gazilion of flashes with some extra lighting screens. The list goes on

Whats wrong with a 5D and L lenses?
Probably me being thick, but thought the full frame would have suited the L Lenses perfectly.

To get wide angle on a 7D you will need something like a 10-22 and they don't come in the L range, wouldn't think a 16-35 would be wide enough given the crop factor

I use the 17-55 IS and that certainly isn't crap even without the L designation, in fact found it better than the 17-40L especially given its f/2.8 with IS

EF-S 10-22 is L quality in all but name – L series are all EF mount only, so they will fit all Canon SLR's

Even then, for most bestest photos you need to use tri-pod, and gazilion of flashes with some extra lighting screen

good luck on using flashes to improve landscapes 🙂

for most bestest photos you need to use tri-pod, and gazilion of flashes with some extra lighting screens. The list goes on

Er… what?